1. Field of Invention
The invention relates to a drive system including a plurality of electric power devices, and more specifically relates to a technique for integrating inverters with a drive system for an electric vehicle or a hybrid vehicle.
2. Description of Related Art
As an example of a known drive system for a hybrid vehicle, Japanese Unexamined Patent Application Publication No. 6-328950 discloses a drive system including two electric power devices (in the present specification, the term “electric power device” generically refers to motors, motor generators, and generators) and a drive case constructed of case segments, each electric power device being contained in one of the case segments. The case segments are combined together such that the two electric power devices are mounted on a common shaft in the drive case, and the size of the drive system is thereby reduced.
Drive systems for a hybrid vehicle or an electric vehicle generally include three-phase brushless electric power devices as the vehicle's drive source and for energy regeneration. When the electric power devices are operated with a direct-current power supply mounted in the vehicle, an inverter having a power module, which includes a switching element, is required for each of the electric power devices (the inverter functions as a converter during energy regeneration by a motor or power generation by a generator). Although the inverters may be arranged separately from their respective electric power devices at suitable positions as they are connected to the electric power devices with power cables, the inverters are preferably integrated with their respective electric power devices for convenience in mounting them in the vehicle.
Currently, however, the maximum operating temperature of the inverters is lower than that of the electric power devices. Therefore, when the inverters are integrated with the drive system as described above, direct heat conduction from the drive system to the inverters must be blocked in some way to protect the inverters. In addition, because the temperature of the inverters increases due to heat emitted from the switching elements included therein, the inverters must be cooled to keep the temperature below the maximum operating temperature. For this purpose, a cooling unit may be disposed between the drive system and the inverters and heat insulation and cooling may be achieved by causing a coolant to flow inside the cooling unit.
When the inverters are integrated with the above-described drive system for a hybrid vehicle or with a drive system for an electric vehicle which includes a plurality of electric power devices, the inverters may be arranged on their respective case segments of the drive case. In this case, however, the coolant's flow path interposed between the drive case and the inverters, for achieving heat insulation and cooling of the inverters, extends across the interfaces between the case segments, and there is a risk that the coolant which flows through the flow path will leak into the drive case along the connection interfaces between the case segments. Such leakage must be prevented as it may lead to a reduction in the insulation performance of the electric power devices.